While the vehicular pollution load in Delhi came down from 7.47 lakh tonnes in 1995-96 to 6.66 lakh tones in 1998-99 (See box), the CPCB adds that the level of sulphur dioxide decreased by 4-40 per cent in the ambient air in Delhi, nitrogen dioxide by 4-13 per cent, particulate matter by 6-17 per cent, carbon monoxide by 3 per cent, and lead by 5-60 per cent. The ambient air quality was tested in industrial areas, residential areas and at traffic intersections.

The CPCB observations are significant because these pollutants are the main culprits invehicular emissions. Carbon monoxide aggravates heart disorders, affects the central nervous system, impairs the oxygen carrying capacity of blood, and is fatal in large doses.

Nitrogen oxides cause irritation of the respiratory tract. Ozone irritates the eyes, nose and throat. It is a risk factor for asthmatics and those involved in heavy exercise. Lead is extremely toxic, affecting the nervous system and blood, and causing hypertension. It can also impair the mental development of children.

Hydrocarbons cause drowsiness, eye irritation and coughing. Aldehydes irritate the eyes, nose and throat, cause sneezing, coughing, nausea and breathing difficulties. And benzene and polycyclic aromatic hydrocarbons are carcinogenic.

Raising the ambient air pollution levels in Delhi even above the WHO guidelines at times, these vehicular pollutants have caused 7,491 premature deaths and 40 lakh hospital admissions annually till date, according to World Health Organization.

The CPCB study emphasises that the majorimpacts on pollution load and air quality have been through switching over to unleaded petrol, reduction of sulphur content in diesel, tightening of vehicular emission norms, use of low-smoke 2T oil, and phasing out of old polluting vehicles.

Elaborating further, the study adds that the progressive reduction of lead content in petrol (from 0.56 gm/ litre to 0.15 gms/ litre), introduction of unleaded petrol for new passenger cars from April 1995, and supply of only unleaded petrol to all vehicles from September 1998 have reduced the content of lead in the vehicular exhaust.

The lead content at traffic intersections has come down by more than 60 per cent. The level of benzene continues to be a cause of concern though, points out the study. The ambient air quality monitoring data indicates high levels of benzene and polyaromatics before and after the introduction of unleaded petrol. This is despite the fact that the benzene content in unleaded petrol is not supposed to be more than 5 per cent (v/v) asprescribed for leaded petrol in 1996. Though refineries are supposed to bring benzene content down to 3 per cent (v/v) by 2000, the study says that it's necessary to reduce it further to less than 1 per cent.

Sulphur content in diesel was reduced to 0.5 per cent in 1996, and to 0.25 per cent in 1997, thereby reducing sulphur dioxide emissions. But it needs to be brought down further to cater to emission norms beyond Euro II, says the study.

From April 1995 onwards, new passenger cars in the Capital came fitted with pollution reducing catalytic converters. The study adds that the Supreme Court order requiring passenger and diesel cars to meet Euro I and Euro II norms from June 1999 and April 2000, respectively, will bring down vehicular pollution further.

Other factors contributing to reduction in the air pollution levels in the city include introduction of low smoke 2T oil, which is one of the causes of pollution from 2-stroke engines, from April 1999. To prevent the use of 2T oil in excess of therequired quantity, pre-mixed 2T oil dispensers have been installed in all Delhi's petrol filling stations.

Lastly, the phasing out of 15-year-old vehicles from December 1998 also contributed to a reduction in Delhi's air pollution.

The board has further recommended various measures for containing vehicular pollution. These include improvement of the public transport system, optimisation of traffic flows and improvement in traffic management by having area traffic control systems, no-traffic zones and green corridors. Traffic management can be also improved by removing road encroachment and regulating construction activities, adds the study.

Other measures include comprehensive inspection and certification for on-road vehicles, and phasing out of grossly polluting vehicles. Besides fuel quality improvements, tightening of emission norms, improvement in vehicle technology, checking adulteration of fuel, checking evaporative emissions from storage tanks and fuel distribution system have also beenrecommended in the study. Going by the fact that most of the earlier initiatives taken at the behest of the CPCB have made such a difference as the study claims, there should be no delay in following up the new recommendations.